High tunnels help increase the profitability of family farms in five ways: 1) by extending the production season 2) by increasing the quality and shelf life of the horticultural crop being produced 3) by minimizing the use of pesticides 4) by ensuring a continuous flow of product when the outside environment is not favorable for field production 5) by increasing the opportunity to grow more value-added and specialty products. Vegetables Extended field production of horticultural crops and in particular vegetables is difficult because of the extreme fluctuations in temperature and moisture – the two most significant environmental factors controlling plant growth. Growers producing vegetables have been using some type of environmental modification in the form of plastic mulch, drip irrigation, row covers or low tunnels to mitigate the effects of cool temperatures or fluctuations in moisture. In the United States and other countries where short growing seasons occur, substantial periods of temperature and moisture extremes represents a major limitation on crop productivity and an invitation for a host of insect and disease organisms to infest a stressed crop. This has led growers in these countries to look at other technologies such as modified environmental structures for intensive production of horticultural crops. The use of high tunnels for production of horticultural crops in the United States offers growers several advantages: 1) reduce temperature and moisture fluctuations during the growing season, 2) lessen disease and insect pressure and enable the use of biological pest control for both insect and disease control, 3) extend the Spring and Fall growing seasons 4) enable the production of crops that have a time to maturity beyond normal field production practices, 5) provide more precise control over water and nutrient application to optimize crop yield and quality as well as reduce non-point source pollution, 6) reduce/eliminate wind stress to plants, and 7) deter animals . Small Fruits Season extension technologies have been used with small fruit, but most of the utilization has been for strawberries . Strawberries have been shown to produce extremely high yields in winter when grown in a vertical system in greenhouses. Winter greenhouse raspberry production has been investigated in New York. However, the costs associated with greenhouse small fruit production are higher than those for high tunnel production. Ideal small fruit crop candidates for production in high tunnels are primocane-bearing raspberries and thornless blackberries. In many northern states, early fall frost dates results in only a small portion of the crop of most primocane-bearing raspberry cultivars being harvested. High tunnel production would extend the period during which raspberries could be harvested for a much longer period of time, increasing profitability greatly for the grower. Under field conditions, thornless blackberries often suffer damage to the flower blossoms during periods of low winter temperatures. Low-temperature mitigation would improve the percentage of the crop that would be harvested, or in some cases, make production possible. A preliminary trial of primocane-bearing raspberries and blackberries in a containerized system, while only recently established, has shown improved plant growth over that of in-ground plants (unpublished data). Through the use of greenhouses and/or high tunnels for primocane- and floricane-bearing raspberries and blackberries, it would be possible to have year-round bramble production in the Mid-Atlantic States. Constant supply is helpful in increasing willingness of buyers to purchase produce from a particular source. 20.3 Regionalized Production of Vegetables 623

Cut flowers Production of cut flowers in the field had been increasing with many of these flowers destined for local farmer’s markets and roadside markets. During the regular growing season market growers have an ample supply of cut flowers although the quality can be negatively impacted by rainfall. As the fall approaches, the numbers of cut flowers produced begins to decrease rapidly after the first frost. Generally farmer’s markets are operating long past the first frost so a method of extending the production of cut flowers would be very important for the producer of field grown cut flowers; however, information on methods of extending the growing season has been limited. Many researchers have now demonstrated in the last 3 years that cut flower species can be successfully grown in high tunnels for approximately 10 months of the year (Figure 8). GREENHOUSES Because the cost of glass was prohibitive, greenhouse crop production was not fully established in the United States until the introduction of polyethylene. The first plastics were not produced on a commercial scale until 1939. Of these, polyethylene was easy to manufacture, resistant to chemicals, durable, flexible and relatively free of odor and toxicity. In the U.S., the first use of polyethylene as a greenhouse cover occurred in 1948, when the late Professor Emery Myers Emmert at the University of Kentucky, used the material in place of glass. Prior to his use of polyethylene, he designed crude wooden structures over which he placed wooden frames covered with stretched cellophane supported by wires. In these structures, he grew commercial crops of lettuce, tomato, cucumber and bedding plants for several years. The first plastic greenhouse was constructed at the Kentucky Agricultural Experiment Station in 1953 and remained in use until 1959. Its primary appeal was its comparatively low cost of construction and maintenance. Currently, many growers have constructed small to medium size greenhouses (1,500 to 10,000 square feet) using two layers of greenhouse grade polyethylene film (6 mil thick) covering the metal frames and inflated with a small blower to provide stability to the structure under high winds and to increase the insulation value of the plastic films (Figure 9). These smaller greenhouses are generally heated with propane, natural gas, #2 fuel oil, wood or in some cases coal. Greenhouses are generally constructed on a cement or stone base and are considered to be non-movable structures and taxable. In the last 25 years, construction of multiple-bay greenhouses with plastic film for their top or roof has been the standard structure for producing horticultural crops in a large area, 10 to 40 acres. In these large growing structures, the common growing system is some form of hydroponics (using water as a carrier for nutrients). Crops FIGURE 8 Snapdragon production in high tunnel at Penn State High Tunnel Research and Education Facility, Rock Springs, PA. (Photo courtesy of Dr Mike Orzolek – PSU) (This item omitted from WebBook edition) 624 Chapter 20 Growing Vegetables Outdoors